The present invention relates to a method for producing AIMn strip or sheet for producing components by brazing, as well as the products obtained by said method. In particular this method is related to fin materials used in heat exchangers.
A challenge today is to manufacture light-weight components for the automotive market. A lot of research is therefore directed to reduce the weight of heat exchangers by using thinner strip without sacrificing, but instead often improving, other product and manufacturing properties. To be able to do this it is necessary to create new materials with higher post braze strength compared to the alloys presently used but still with adequate corrosion properties. For fins this means that they normally should be sacrificially paired with other parts of the heat exchanger by having a lower corrosion potential than those. The increased fin strength has to be achieved in modern CAB furnaces, which restricts the use of certain alloying elements, like Mg, previously used in strip for vacuum brazing. The fin strip must be easy to handle for the manufacturer and the strip formed to fins are always slightly deformed prior to brazing which puts some requirements on formability in the delivery condition. The fin strip is always delivered in thin, 50-200 μm, and cut narrow strip, making it very difficult to handle if fully soft annealed. Therefore the strip is normally delivered in half hard condition with restricted formability.
To reach higher post braze strength levels is quite complicated without hazarding the brazing performance described as sagging resistance and resistance to liquid core penetration during brazing or the necessary formability when forming the fins out of the strip. Only when these requirements are met consistently by the new materials, this will allow the use of thinner fins with a high post brazed strength, thereby reducing the weight compared to the products used today. In resent years, problems with severe liquid core penetration have occurred when using thin clad fin, especially if using slow braze heating cycles.